MERCURY CONCENTRATIONS IN FISH FROM THE GUADALUPE RIVER, TEXAS: RELATIONSHIPS WITH BODY LENGTH AND TROPHIC POSITION by Taylor Rene Gold Quiros, B.S. A thesis submitted to the Graduate Council of Texas State University in partial fulfillment of the requirements for the degree of Master of Science with a Major in Aquatic Resources December 2018 Committee Members: Jessica Dutton, Chair Tim Bonner Weston Nowlin Clint Robertson COPYRIGHT by Taylor Rene Gold Quiros 2018 FAIR USE AND AUTHOR’S PERMISSION STATEMENT Fair Use This work is protected by the Copyright Laws of the United States (Public Law 94-553, section 107). Consistent with fair use as defined in the Copyright Laws, brief quotations from this material are allowed with proper acknowledgement. Use of this material for financial gain without the author’s express written permission is not allowed. Duplication Permission As the copyright holder of this work I, Taylor Rene Gold Quiros, authorize duplication of this work, in whole or in part, for educational or scholarly purposes only. DEDICATION My Toby. Te amo. I miss you ACKNOWLEDGEMENTS I would first like to thank my thesis advisor Dr. Jessica Dutton; her office was always open whenever I ran into a trouble spot or had a question about my research or writing. Dr. Tim Bonner and Dr. Weston Nowlin were incredibly helpful in teaching me how to think like a scientist and their patience with my questions was without end. Gratitude is also due to Clint Robertson, without whom I wouldn’t have fish to analyze in the first place nor would I know the differences between those pesky sunfish. I would also like to thank Texas State University for funding this study. Many people donated time and effort to help with both field and lab work and I am grateful to each and every one of you: Stacey Britton, Meaghan McCormack, Kristyn Cunningham, and Alexis Lambert. Nina Noreika, you were a wonderful sounding board for many of my more goofy ideas and I thank you for it. Lily - thanks for getting me outside and out of my own head. Lastly, I would like to thank my family who kept me sane, reminded me to eat, and supported me throughout this process. I could not have done this without you. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ................................................................................................ v LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix ABSTRACT ....................................................................................................................... xi CHAPTER I. MERCURY LEVELS IN TROPHICALLY DIVERSE FISH THROUGHOUT THE GUADALUPE RIVER, TEXAS ABSTRACT ................................................................................................ 1 i. INTRODUCTION ................................................................................... 2 ii. METHODS ........................................................................................... 11 iii. RESULTS ............................................................................................ 17 iv. DISCUSSION ...................................................................................... 22 II. EVALUATING THE RELATIONSHIP BETWEEN δ15N AND MERCURY CONCENTRATIONS IN FRESHWATER FISH FROM THE GUADALUPE RIVER ABSTRACT .............................................................................................. 54 i. INTRODUCTION ................................................................................. 55 ii. METHODS ........................................................................................... 60 iii. RESULTS ............................................................................................ 65 iv. DISCUSSION ...................................................................................... 68 vi APPENDIX SECTION ..................................................................................................... 81 LITERATURE CITED ..................................................................................................... 95 vii LIST OF TABLES Table Page 1. Sampling locations for each investigated species with corresponding sample size and percentage water content in muscle tissue ...................... 35 2. Feeding guild allocation for each investigated species ................................................ 38 3. Linear regression results describing the relationship between Hg concentration in muscle tissue and total length for species shownin Figures 2 – 6 .................................... 40 4. Percentage of individuals that exceeded the TDSHS Hg advisory of 0.7 µg/g wet wt and the FDA Hg advisory of 1.0 µg/g wet wt, with the corresponding total length (TL) at which the Hg concentration began to exceed these advisory limits ................................. 42 5.Comparison in Hg concentrations in present study to literature values from Northeast and South Texas ........................................................................... 43 6. Pearson’s correlation coefficient (r) for relationships between Hg concentration and ecological characteristics ............................................................... 75 7. Results of Tukey’s HSD post hoc for differences in Hg concentration between sites .................................................................................... 77 viii LIST OF FIGURES Figure Page 1. Fish collection sites on the Guadalupe River ............................................................... 44 2. Relationship between total length and Hg concentration in muscle tissue for low trophic level (planktivore, herbivore, detritivore, and planktivore/detritivore) species ......................................................................................... 45 3. Relationship between total length and Hg concentration in muscle tissue for moderate trophic level (invertivore, invertivore/herbivore, and invertivore/detritivore) species in the Mugilidae and Centrarchidae families .................. 46 4. Relationship between total length and Hg concentration in muscle tissue for moderate trophic level (invertivore, invertivore/herbivore, and invertivore/detritivore) species in the Cyprinidae, Characidae, and Castomidae families ..................................... 47 5. Relationship between total length and Hg concentration in muscle tissue for high trophic level (carnivore and invertivore/carnivore) species in the Ictaluridae and Lepisosteidae families .............................................................................. 48 6. Relationship between total length and Hg concentration in muscle tissue for high trophic level (carnivore and invertivore/carnivore) species in the Centrarchidae family ................................................................................................... 49 7. Mean Hg concentration in muscle tissue for all species designated as low, moderate, and high trophic levels for all five Guadalupe River sites combined. .............................. 50 8. Mean Hg concentration in low, moderate, and high trophic level species at the five investigated sites ......................................................................... 51 9. Mean Hg concentration in three commonly consumed bass species with n ≤ 5: Guadalupe bass (GB), white bass (WB), and striped bass (SB) ....................................... 52 10. Map showing the location of the investigated study sites in relation to ecoregion ..................................................................................................... 53 11. Mean muscle Hg concentration among sites at estimated trophic levels (ETLs) 2 - 2.99, 3 - 3.99, 4 + ................................................. 78 ix 12. Relationship between log10 [Hg] and estimated trophic level at each site .................. 79 13. Mean Hg muscle concentration at each site for six fish species ................................. 80 x ABSTRACT Mercury (Hg) is known to bioaccumulate over time in freshwater fish and biomagnify up freshwater food webs, so top predatory fish have the highest Hg body burden. Within Texas, Hg studies in freshwater fish have primarily focused on the northern half of the state and south Texas is relatively understudied. This study investigated the concentration of Hg in muscle tissue from 41 trophically diverse species (n = 1,772) in relation to body length and trophic position at five sites on the Guadalupe River in South Central Texas using a direct mercury analyzer and stable isotope analysis (δ13C, δ15N). The majority of fishes showed a positive relationship between body length and Hg concentration, indicating that Hg was bioaccumulating over time. Striped mullet was the only species that displayed an inverse relationship suggesting growth dilution is occurring. Mercury concentrations were higher in top predators including longnose gar, flathead catfish, and striped bass, and lower in moderate and low trophic level fishes, including Mexican tetra, threadfin shad, and suckermouth catfish. Within the five sites examined, the average Hg concentration in each species was higher in reservoir sites than riverine sites. There was a positive relationship (p < 0.05) between δ15N and Hg concentration at 4 of the 5 sites, indicating that Hg biomagnification is occurring at these sites. The biomagnification factor differed between sites, however it was not positively